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Chapter 8Final conclusions pWe have seen that results obtainable using the simulation model were in goodagreement with theoretical results, with a maximum deviation of 3% for mean accessdelays and 2% for throughput. In this analysis it was found that the scheduler-lookahead is the major delay element in the transmission cycle, which dramatically reducesthe throughput.In chapter 5, before a performance optimisation or the incorporation of newmechanisms was approached, we first presented a rigorous performance evaluation ofthe fundamental properties of the DVB/DAVIC protocol, based on a 3 Mbps upstreamchannel.The first issue addressed was the protocol efficiency and performance characteristics interms of global offered load. Simulation results revealed that for the exponential backoffalgorithm, the protocol can sustain linear throughput increase and bounded delays foroffered loads up to 61% of the cc. The maximum system throughput was even higherand reached ≈ 65%. However, in order to achieve this throughput, the offered loadneeds to be higher that 70% of the cc at which point frame delay becomes unbounded.This throughput is higher when compared to other pure random access mechanisms,such as Aloha (37%), and CSMA/CD (60%), [117]. The main advantage is that thethroughput maintains maximum values even under heavy traffic loads and does notdegrade as rapidly as these other random access protocols.A similar performance characteristic with linear throughput and delay increase wasconfirmed in the following scenario studied (capacity in terms of active stations), wherean increased node population was considered. Here, the maximum sustainablethroughput was also 61% of the cc, with bounded access delays under 40 ms. Resultsfor the splitting tree algorithm revealed that this algorithm could achieve a highersystem performance than the exponential backoff algorithm, achieving a maximumsystem throughput of up to ≈ 65% of the cc.In addition, for these two analyses (offered load scalability and capacity in terms ofactive stations) the maximum channel utilisation achieved by the protocol was ≈ 90% ofthe channel capacity. The difference between maximum system throughput andutilisation is attributed to the extensive protocol overhead involved, generated by the8-4